linux-kernel - Re: [PATCH] thp: reduce khugepaged freezing latency

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Date:	Wed, 9 Nov 2011 07:53:42 -0800
From:	Tejun Heo <tj@...nel.org>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	"Rafael J. Wysocki" <rjw@...e.com>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jiri Slaby <jirislaby@...il.com>,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] thp: reduce khugepaged freezing latency

Hello, Andrea, Srivatsa.

On Wed, Nov 09, 2011 at 06:15:38PM +0530, Srivatsa S. Bhat wrote:
> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> >> index 4298aba..67311d1 100644
> >> --- a/mm/huge_memory.c
> >> +++ b/mm/huge_memory.c
> >> @@ -2277,6 +2277,7 @@ static struct page *khugepaged_alloc_hugepage(void)
> >>  		if (!hpage) {
> >>  			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
> >>  			khugepaged_alloc_sleep();
> >> +			try_to_freeze();
> >>  		} else
> >>  			count_vm_event(THP_COLLAPSE_ALLOC);
> >>  	} while (unlikely(!hpage) &&
> >> @@ -2331,7 +2332,7 @@ static int khugepaged(void *none)
> >>  {
> >>  	struct mm_slot *mm_slot;
> >>
> >> -	set_freezable();
> >> +	set_freezable_with_signal();
> >>  	set_user_nice(current, 19);

Oooh, please don't do that.  It's already gone in the pm tree.  It
would be best if wait_event_freezable_timeout() can be used
(ie. wakeup condition should be set somewhere) but, if not, something
like the following sould work.

static void khugepaged_alloc_sleep(void)
{
	DEFINE_WAIT(wait);
	add_wait_queue(&khugepaged_wait, &wait);
	try_to_freeze();
	schedule_timeout_interruptible(
			msecs_to_jiffies(
				khugepaged_alloc_sleep_millisecs));
	try_to_freeze();
	remove_wait_queue(&khugepaged_wait, &wait);
}
												
Thanks.

-- 
tejun
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